At present, Global System for Mobile communications (GSM) and Code Division Multiple Access (CDMA) are major communication technologies for portable terminals. Most of Europe uses GSM, whereas CDMA is the most dominant standard in the U.S. Modifications of GSM and CDMA are also used. In some areas, a plurality of communication technologies is used jointly or in combination, for portable terminals. Recent portable terminals support dual modes so that a plurality of communication networks can be used with a single portable terminal.
A dual-mode portable terminal cannot use a communication network until the dual-mode portable terminal is completely booted to the communication network, taking much time. Therefore, the selective use of a communication network causes inconvenience to a dual-mode portable terminal user. For example, a dual-mode portable terminal supporting CDMA and GSM communication networks needs to be booted in CDMA mode, for using the CDMA communication network. For using the GSM network later, the dual-mode portable terminal should be switched to GSM mode through rebooting. As much time is taken for rebooting, the dual-mode portable terminal is not so convenient to the user.
To overcome the inconvenience caused by the dual-mode portable terminal, a dual-standby portable terminal was proposed. Unlike the dual-mode portable terminal that is booted to a single communication network, the dual-standby portable terminal simultaneously supports a plurality of communication networks (e.g. CDMA and GSM communication networks).
Such a dual-standby portable terminal has limitations in actual calls. Since common parts such as a microphone and a speaker used for outputting voice during a voice call or ringtones and bell sound during data communication cannot be used simultaneously, if the common parts are in use in one communication mode, a possible communication request of another communication mode cannot be notified to a user.
For example, even though a communication request (e.g. a voice call request) is generated from the GSM communication network during a voice call over the CDMA communication network, it is difficult to notify the user of the communication request from the GSM communication network because the common hardware like the microphone and the speaker are in use for the on-going voice call.